For (x-)blockdev-create, all protocol drivers that support image creation also need to offer a .bdrv_truncate() implementation that matches in features. A previous series of mine brought gluster's and sheepdog's implementation up to par regarding preallocated truncation; but I forgot about drivers that have a .bdrv_create() but no .bdrv_truncate() at all.
There is only one of these, and that is ssh. Since libssh2 does not seem to know any way of truncating files, we can only support growing files -- but that is what we need for (x-)blockdev-create. Note that there are also drivers which do not support growing files, namely iscsi and file-posix for host devices (maybe more? I hope not). But these also pretty much ignore the specified size on .bdrv_create() and just use the size of the existing device. They just check that the specified size does not exceed the actual size, so that pretty much matches what their .bdrv_truncate() supports, and we should be fine there. Max Reitz (3): block/ssh: Pull ssh_grow_file() from ssh_create() block/ssh: Make ssh_grow_file() blocking block/ssh: Add basic .bdrv_truncate() block/ssh.c | 61 +++++++++++++++++++++++++++++++++++++++++++++++++++++-------- 1 file changed, 53 insertions(+), 8 deletions(-) -- 2.14.3